If your OHQs are separate from their units, another option is to rearrange who’s attached to whom. You can do this with the “unit administration” tab of the subordinate unit, I think.
Also, it helps to give each OHQ a really bright color that’s easily distinguishable from nearby OHQs. (I think you do this in the unit admin screen of the OHQ.) So I’ll have a bright red fighting next to a bright green. Not only does it make command & control easier, but it’s nice eye candy. :)